Advances in software, computers and networking systems have created many new and useful ways to distribute, utilize and access content items (e.g., audio, visual, and/or video signals). Content items are more accessible than ever before. As a result, however, content owners and users have an increasing need to identify, track, manage, handle, link content or actions to, and/or protect their content items.
These types of needs may be satisfied, as disclosed in this application, by generating a signature of a content item (e.g., a “content signature”). A content signature represents a corresponding content item. Preferably, a content signature is derived (e.g., calculated, determined, identified, created, etc.) as a function of the content item itself. The content signature can be derived through a manipulation (e.g., a transformation, mathematical representation, hash, etc.) of the content data. The resulting content signature may be utilized to identify, track, manage, handle, protect the content, link to additional information and/or associated behavior, and etc. Content signatures are also known as “robust hashes” and “fingerprints,” and are used interchangeably throughout this disclosure.
Content signatures can be stored and used for identification of the content item. A content item is identified when a derived signature matches a predetermined content signature. A signature may be stored locally, or may be remotely stored. A content signature may even be utilized to index (or otherwise be linked to data in) a related database. In this manner, a content signature is utilized to access additional data, such as a content ID, licensing or registration information, other metadata, a desired action or behavior, and validating data. Other advantages of a content signature may include identifying attributes associated with the content item, linking to other data, enabling actions or specifying behavior (copy, transfer, share, view, etc.), protecting the data, etc.
A content signature also may be stored or otherwise attached with the content item itself, such as in a header (or footer) or frame headers of the content item. Evidence of content tampering can be identified with an attached signature. Such identification is made through re-deriving a content signature using the same technique as was used to derive the content signature stored in the header. The newly derived signature is compared with the stored signature. If the two signatures fail to match (or otherwise coincide), the content item can be deemed altered or otherwise tampered with. This functionality provides an enhanced security and verification tool.
A content signature may be used in connection with digital watermarking. Digital watermarking is a process for modifying physical or electronic media (e.g., data) to embed a machine-readable code into the media. The media may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media signals such as images, audio signals, and video signals. However, it may also be applied to other types of media objects, including documents (e.g., through line, word or character shifting), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems typically have two primary components: an encoder that embeds the watermark in a host media signal, and a decoder that detects and reads the embedded watermark from a signal suspected of containing a watermark (a suspect signal). The encoder embeds a watermark by altering the host media signal. And the decoder analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
Several particular watermarking techniques have been developed. The reader is presumed to be familiar with the literature in this field. Particular techniques for embedding and detecting imperceptible watermarks in media signals are detailed in the assignee's co-pending patent application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914) and in U.S. Pat. No. 5,862,260, which are referenced above.
According to one aspect of our invention, the digital watermark may be used in conjunction with a content signature. The watermark can provide additional information, such as distributor and receiver information for tracking the content. The watermark data may contain a content signature and can be compared to the content signature at a later time to determine if the content is authentic. As discussed above regarding a frame header, a content signature can be compared to digital watermark data, and if the content signature and digital watermark data match (or otherwise coincide) the content is determined to be authentic. If different, however, the content is considered modified.
According to another aspect of the present invention, a digital watermark may be used to scale the content before deriving a content signature of the content. Content signatures are sensitive to scaling (e.g., magnification, scaling, rotation, distortion, etc.). A watermark can include a calibration and/or synchronization signal to realign the content to a base state. Or a technique can be used to determine a calibration and/or synchronization based upon the watermark data during the watermark detection process. This calibration signal (or technique) can be used to scale the content so it matches the scale of the content when the content signature was registered in a database or first determined, thus reducing errors in content signature extraction.
These and other features and advantages will become apparent with reference to the following detailed description and accompanying drawings.